1. Field of the Invention
The present invention relates to electrostatographic reproduction machines such as copiers and printers, and more particularly to a device for scavenging charged carrier particles from an image-bearing surface of such a copier or printer.
Electrostatographic process machines such as copiers and printers are well known for producing or reproducing toned images on selected substrates by employing electrostatic charges and toner particles on an image-bearing surface (IBS) such as a photoconductive surface. Typically, such machines operate through a sequence of currently well known electrostatographic process steps. In copier or printer type machines, for example, these steps include (1) charging of an insulated photoconductive surface with electrostatic charges, (2) forming a latent image electrostatically on such surface by selectively discharging areas on such surface, (3) developing the electrostatic image so formed with particles of toner contained in developer material, (4) transferring the toned image to a suitable receiver sheet for fusing thereon by a fusing apparatus to form a hard copy, and (5) cleaning the photoconductive surface by removing residual toner and/or other particles therefrom in preparation for similarly reusing such surface to produce another such image.
Unfortunately, as is well known, charged carrier particles contained in multiple component developer material undesirably also transfer along with the toner particles and are attracted onto the latent image area of the image bearing surface during the development step. Unlike toner particles which are fusible, such carrier particles are not fusible, and hence when transported through the fusing step, end up creating image defects such as black spots, image voids and halftones.
2. Description Relative to the Prior Art
Apparatus for attempting to scavenge or remove such carrier particles from the developed toner image prior to the fusing step are disclosed for example in U.S. Pat. No. 4,918,488 issued Apr. 17, 1990 to Creveling et al; U.S. Pat. No. 3,543,720 issued Dec. 1, 1970 to Drexler et al; and U.S. Pat. No. 3,457,900 issued Jul. 29, 1969 also to Drexler et al. Such disclosed scavenging apparatus or devices typically include a pickup surface area thereof onto which the charged carrier particles are attracted from the image-bearing surface of their host copier or printer. Where the means of such attraction is electrical biasing, it has been found for example: a) that the voltage across the image-bearing surface is significantly non-uniform and can vary between 30-40 volts within a short time interval, and (b) that an electrically and appropriately biased pickup surface area undesirably may actually recharge and hence reverse the polarity of attracted carrier particles thereby causing such particles with the reversed or wrong sign polarity to be re-attracted onto the image-bearing surface of the copier or printer where they once again are likely to cause image defects as discussed above.